Hi I have just posted this on another thread, you could see if this also applies to you?
"Hi. I've joined this forum because I have a very similar problem.
I have a 1.5 diesel saxo. For no reason and randomly, the handbrake warning light comes on, at the same time the rev counter stops working. The rev counter suddenly starts working and the handbrake warning light goes out randomly too.
I have noticed that if the engine is running and I turn my sidelights on, then turn on the front foglamps, then turn the foglamps back off the rev counter starts working and the handbrake warning light goes off. This works 90% of the time.
I've yet to see if this fix is when I'm accelerating, decelerating or constant load etc. It doesn't fix it if I turn the headlights on.
At some point in 2012 handbrake warning light being on is an MOT failure. You just know that when its in for an MOT the bast*d light will come on! So if I can't sort this out the bulb is coming out lol"